Non-contact temperature measurement is required for many objects. Conventional infrared radiation sensors determine temperature of a viewed target based on measured heat flux from the target, an emissivity of the target, and the temperature of the sensor. If the target surface has a known emissivity, then the temperature of the target can be accurately measured based on the known emissivity and the output of the radiation sensor. Emissivity can vary from material to material and from surface to surface. Where emissivity of a target is unknown, emissivity can sometimes be assumed, and some techniques exist for decreasing measurement uncertainties due to emissivity assumptions.